With each data release, the Sloan Digital Sky Survey collaboration has published a Data Release paper, which describes the data, the data acquisition process, and other details of the project. The most current public data release of the SDSS-III is Data Release 8 (DR8), which was released in January 2011.
The Data Release 8 paper describes the details of DR8. The Early Data Release (EDR) paper, which came out after the first data from the original Sloan Digital Sky Survey became public, contains the most detailed description of data from the original SDSS.
The Eighth Data Release of the Sloan Digital Sky Survey: First Data From SDSS-III
Aihara, H., et al., 2011. Astophysical Journal Supplements, 193(29), 1-17.
Erratum: 2011, Astrophysical Journal Supplements, 195(26), 1-4.
The Seventh Data Release of the Sloan Digital Sky Survey
Abazajian, K. N., et al., 2009. Astophysical Journal Supplements, 182, 543-558.
The Sixth Data Release of the Sloan Digital Sky Survey
Adelman-McCarthy, J. K. et al. 2008, Astophysical Journal Supplements, 175(2), 297-313.
The Fifth Data Release of the Sloan Digital Sky Survey
Adelman-McCarthy, J. K. et al. 2007, Astophysical Journal Supplements, 172(2), 634-644.
The Fourth Data Release of the Sloan Digital Sky Survey
Adelman-McCarthy, J. K. et al. 2006, Astophysical Journal Supplements, 162(1), 38-48.
The Third Data Release of the Sloan Digital Sky Survey
Abazajian, K. N. et al. 2005, Astronomical Journal, 129(3), 1755-1759.
Sloan Digital Sky Survey Imaging of Low Galactic Latitude Fields: Technical Summary and Data Release
Finkbeiner, D. P. et al. 2004, Astronomical Journal, 128(5), 2577-2592.
The Second Data Release of the Sloan Digital Sky Survey
Abazajian, K. N. et al. 2004, Astronomical Journal, 128(1), 502-512.
The First Data Release of the Sloan Digital Sky Survey
Abazajian, K. N. et al. 2003, Astronomical Journal, 126(4), 2081-2086.
Sloan Digital Sky Survey: Early Data Release
Stoughton, C., et al., 2002. Astronomical Journal, 123(1), 485-548.
Erratum: 2002, Astrophysical Journal Supplements, 123(6), 3487.